The present invention relates to a center lifting device for lifting and transferring rolls of material, such as paper rolls and the like, comprising two parts, one inside the other, which can be moved over a limited distance in relation to each other and fitted partly into the hollow or care of the roll of the material. The upper end of the inner part is attached to the lifting device and the lower end of the outer part includes a gripping member which expands and contracts under the effect of movement between the parts, for attaching the center lifting device to the hollow in the roll of the material. The outer part has at its upper end a bolt device for preventing the inner part from rising in relation to the outer part.
Previously known is a conveying device for conveying paper rolls, comprising a bar-like inner part attached to the lifting device and a surrounding tubular outer part. The inner part is attached to the lifting device by means of lever arms, which are fitted to produce, during lifting, an axial movement between the inner and outer parts, whereby the conical piece at the lower end of the inner part rises along with the inner part and forces the turning bolts at the lower end of the outer part outwards to attach the conveying device to the socket in the center of the paper roll. After conveying, the paper roll is lowered, whereby the inner part can descend in relation to the outer part and the conical piece at the lower end of the inner part no longer presses the turning bolts outwards. In order to detach the conveying device and to lift it out of the socket, the inner part must, however, be locked in relation to the outer part. This is achieved by means of a spring-actuated bolt device which, when released, pushes itself onto the inner part at the upper end of the outer part, thereby preventing it from rising in the outer part. On top of the bolt device there is a screwable lid which can be turned away from the front of the bolt device in order to release it and turned back in order to force the bolt device off the top of the inner part.
This known conveying device is very complicated and expensive. In addition, it has the disadvantage that it is difficult to make the turning bolts grip the socket firmly enough at the initial stage of the lifting, and the turning cover must also be opened manually at the end of the lift.
The object of the present invention is thus to provide a center lifting device of the type mentioned in the preamble, wherein the said drawbacks are eliminated. The center lifting device can be attached directly to the inner part without any lever arms; the center lifting device grips the socket so firmly even at the beginning that the gripping member at its lower end can be expanded to produce a sufficient friction force for lifting, and at the end of the lift the bolt device automatically locks the inner part in relation to the outer part so that the center lifting device can be lifted out of the socket.